As I've said a few times, including quite recently on this website, the No 4 rifles were designed so that, in production, the barrel could simply be screwed into place and then the semi-skilled operator would select a bolt head, made in a range of nominal lengths, until the headspace was in spec. There was no other reason for making boltheads in different lengths, and all the stories about actions stretching and so forth are, as flintlocke said, nonsense. Having said that, a mismatched bolt may not result in headspace being in spec., and will drop the value.
As a general thing though, the chambers on Lee Enfield rifles can be a bit big, and tolerances a bit loose, to allow the rifles to function even with ammunition which is a bit grotty or dented. This is perhaps especially the case with wartime production. They were never intended to be used with reloads.
As a result, brass life can be a bit short if, and this is important, you reload according to some of the practices which appear common. Full length resizing, for example, will soon put paid to your brass in most Lee Enfields, as the brass will tend to stretch and eventually separate - sometimes in as little as a couple of loading cycles. It can also bulge unevenly in a loose chamber.
What I find works well is to pay careful attention to fireforming the first time you fire your loads with new brass. I used to put a narrow band of masking tape around the case just in front of the rim, but a suitably-sized O-ring works just as well and is less effort. The idea is to hold the case both concentric with the bore and hard against the bolt-face on the first firing. This way, it fireforms symmetrically and the shoulder expands out to fill the chamber. This avoids having to make a false shoulder, and also can be done with factory loads.
From there on, if you only neck size (I like the Lee Collet dies for this), the brass will headspace on the shoulder, and it won't stretch. As a result you get excellent case life.
